This invention relates generally to laser scanners and more particularly to integral hand-held laser scanners.
Laser scanners have been disclosed in the patent literature and some are commercially available for use in reading bar codes, such as the Uniform Product Code (UPC). Such scanners commonly make use of a laser tube mounted in a scanning head adapted to be mounted or held over the bar code symbol to be scanned. The laser tube generates the laser light beam which is directed through an optical assembly out of the head to impinge the symbol. In most applications the exiting laser beam is caused to quickly move across (traverse) the symbol while the device's head is held stationary with respect to the symbol. The optical assembly is arranged to provide proper focusing of the beam to get maximum depth of field with appropriate beam width in order to resolve the bars making up the bar code over a working distance, i.e., the distance between the bar code and the head. The laser beam traversing the bar code is reflected off the material on which the code is printed. If that material is not spectral, e.g., is paper, the light reflects and scatters in all directions in an evenly distributed fashion off of the material. Some of that reflected light scatters back into the laser scanning head and associated optical components for receipt by a photocell and associated signal processing components. The photocell and the associated signal processing components produce electrical signals indicative of the detection of the bars making up the code. This signal is then digitized for use by associated decoding circuitry to provide a signal indicative of the information contained in the code.
As is known, the Federal Bureau of Radiological Health has defined five classes of laser devices, four of which classes require some type of labeling on the devices themselves. Such classes are generally defined on the basis of power output of the devices, with the more powerful laser devices requiring a higher degree of warning on the label. For example, the lowest power category is a Class 1 laser device. Such a device does not present any threat to health or safety and therefore does not require any label whatsoever. Class 2 laser devices, that is devices of the next higher power category are classified to be of a minimal hazard and thus require a label. However, the label required is a simple cautionary one bearing the symbol of a starburst and the words "Caution: Do not stare into the beam". A Class 3 laser is one which is of substantially higher power and which poses a distinct ocular hazard but no hazard to other parts of the body and thus has to bear a "DANGER" type of label. Classes 4 and 5 type lasers are increasingly hazardous and thus require total constraint so that the beam cannot escape for exposure to the human body.
Laser scanners which include hand-held scanning heads for use in reading bar codes, by their unconstrained nature, have the potential for exposing operation personnel or others to the scanning laser beam. Accordingly, it is desirable to make such scanning devices of sufficiently low power so as not to present any exposure hazard. Obviously, in this regard, it is preferable to produce a device which falls into the Class 1 category. However, as will be appreciated by those skilled in the art, the problem with using such low-powered lasers is that they produce such a small amount of light for reflection off the bar code, that they would require either very large optical components or would have to include very sensitive signal processing means to overcome the severe signal-to-noise ratio problems inherent in low reflected light situations.